THE MEDITERRANEAN LOWER CRETACEOUS

С. emerici has not been found in the neostratotype and that H. astierianum is rare,
is not substantiated from the viewpoint of biostratigraphic theory.
The lower boundary of the Barremian is very disputable. A number of authors
include the P. angulicostata in the base of the Barremian (Рентартен, 1951;
Луппов, 1952; Мордвилко, 1960-1962; Э р и с т а в и, 1960). In Bulgaria
this opinion is maintained by Breskovski (1975). The grounds for this
view are that in some sections in clayey-carbonate facies from the shelf zone in
beds with P. angulicostata the first Barremian ammonites appeared (early Barremites).
In the pelagic facies the successions are clearly differentiated and usually
the P. angulicostata Zone is characterized by a homogeneous association. However,
it is poorer than the synchronous association in the shelf clayey-carbonate facies.
Evidently, the difficulties here are objectively conditioned by the factors controlling
the ammonite distribution (Table 8).
2.4.1. Substages
On the basis of the intrinsic regularities in the ammonite successions, the Barremian
is divided into two substages: Lower and Upper Barremian.
The Lower Barremian is characterized by ammonites from the group of Crioceratites
emerici, Holcodiscus, Haplocrioceras, Acrioceras, Spiticliscus, Salfeldiella,
Biasaloceras, Uhligia, Protacrioceras, Anahamulina, Hamulina, etc.
The Upper Barremian is distinguished by the extensive development of Barremites,
Pseudosaynella, Heteroceras, Imerites, Jaubertites, Karsteniceras, Paraspinoceras,
Hamulina, Anahamulina, Pseudohaploceras, Silesites, Pulchellia, Subpulchellia,
Carstenia, etc.
2.4.2. Biostratigraphic Zones
In the Barremian the biostratigraphic zones are identified according to different
fossil groups.
Ammonite Zones
There are two standard ammonite zones in the accepted volume of the Barremian,
namely: Crioceratites emerici and Heteroceras astierianum (Table 9).
C. emerici Zone. It is based on the Range-zone of the index species. Its lower
boundary is marked by the appearance of this species which has ubiquitous distribution.
The main characteristic of the zone is determined by Crioceratites emerici L é v.,
C. thiollieri (A s t.), С. razgradi (T о u 1 a), Acrioceras tabarelli (A s t.), A. silesiacum
(U h 1.), A. furcatum (d'O г b.), Pseudothurmannia pseudomalbosi (S a г.,
S с h ô n d.), P. simionescui S a г., Hamulina dissimilis (d'O r b.), H. koeneni
D i m., Holcodiscus perezianus (d'O r b.), H. rarecostatus (К a г.), H. geronimaeformis
T z., H. diversicostatus (С о q.), H. sophonisba (С о q.), H. caillaudianus
(d'O г b.), H. ziezac К a г., Anahamulina subcylindrica (d'O r b.), Barremites
difficilis (d'O r b.), B. karakaschi (S i m.), Spitidiscus seunesi (K i 1.), S. douvillei
(N i с k.) and Astieridiscus morleti (K i 1.).
H. astierianum Zone. It is based on the Concurrent-Range-zones of Heteroceras
astierianum, Pseudosaynella strettostoma, Silesites seranonis and B. cassidoides.
Its lower boundary is marked bilaterally by the disappearance of the typical elements
of the C. emerici and P. strettostoma, etc.
The zone is characterized by a very rich association: H. astierianum d'O г b.,
H. bifurcatum d'O r b, Imerites varnensis N i k., I. giraudi К i 1., /. densocostatus
R e n n g., Colchidites securiformis S i т., C. colchicus D j., C. intermedius D j.,
Jaubertites dubius S а г k., Matheronites barremensis (U h 1.), M. hammatoptychus
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